my brother was on prozac when he was like 17, and he experienced fatigue also. he stopped taking it after a few weeks though.
i took prozac also, but it made me feel like i was on speed! my house was SO clean. i stopped it though cuz i still felt very depressed.
zoloft makes me fatigued, and so do antianxiety meds ive tried like valium, xanax, and serax.
right now i self medicate with different meds ive collected, i take serax to reduce hypomania, but it makes me so tired that i compensate with lots of pepsi. plus, sometimes when im on meds i dont eat, and that totally contributes to the fatigue.

i guess everyone justs responds differently to meds.